1. Technical Field
The present disclosure relates to a retinal prosthesis.
2. Discussion of the Related Art
As is known, there are now available numerous retinal prostheses, which are electronic systems with medical purposes, designed for persons having visual impairments.
In general, a retinal prosthesis performs the function of making up, at least in part, for a reduced functionality of the retina, caused by a pathological condition of the retina itself, such as, for example, retinitis pigmentosa.
In greater detail, retinal prostheses are divided into retinal prostheses of an epiretinal type and retinal prostheses of a subretinal type. In use, prostheses of an epiretinal type are arranged, at least in part, on the surface of the retina that is exposed to the light, hence on the surface of the retina facing the crystalline lens. Instead, prostheses of a subretinal type are arranged, at least in part, between the retina and the so-called retinal pigment epithelium, which is the layer of pigment cells that is located on the outside of the retina itself.
This said, irrespective of the type, retinal prostheses each comprise a respective internal unit and a respective external unit. In use, the external unit is set externally with respect to the eye, whereas the internal unit is set inside the eye, and in particular within the vitreous body.
By way of example, FIG. 1a shows a retinal prosthesis 1, the external and internal units of which are designated, respectively, by 2 and 4.
The external unit 2 comprises a transmitter 6 and a first antenna 8, which is electrically connected to the transmitter 6 and is formed, for example, by a coil made of conductive material.
The internal unit 4 comprises a second antenna 10, which is also formed, for example, by a coil of conductive material. Furthermore, the internal unit 4 comprises an integrated electronic device 12 and an electrical connection cable 14, which connects the second antenna 10 to the integrated electronic device 12; for example, the electrical connection cable 14 can be a flexible electrical bus.
The integrated electronic device 12 functions as artificial retina and comprises a plurality of photodetectors 18 (FIG. 1b), an electronic circuitry 19 (FIG. 2), and a plurality of electrodes 20 (FIG. 1b).
As shown in greater detail in FIG. 1b, the integrated electronic device 12 has substantially the shape of a parallelepiped and has a bottom surface 12a and a top surface 12b. The photodetectors 18 face the top surface 12b so as that they can be reached by the light coming from the outside world, whilst the electrodes 20 extend underneath the bottom surface 12a. In turn, the bottom surface 12a is constrained, for example by means of an appropriate adhesive layer (not shown), to the electrical connection cable 14, which, in practice, carries the integrated electronic device 12.
As shown in greater detail in FIG. 2, the electronic circuitry 19 is electrically connected to the photodetectors 18 and to the electrodes 20. Furthermore, the electrical connection cable 14 comprises at least a first conductive element 14a and a second conductive element 14b, and an insulating sheath 14c, which envelops the first and second conductive elements 14a, 14b and carries the integrated electronic device 12. The first and second conductive elements 14a, 14b are electrically connected to the electronic circuitry 19, for example by means of a first via 21a and a second via 21b, respectively. In addition, the first and second conductive elements 14a, 14b are electrically connected, respectively, to a first terminal and a second terminal of the second antenna 10. Furthermore, the first and second conductive elements 14a, 14b, the insulating sheath 14c, and the electrodes 20 are such that the electrodes 20 themselves traverse the electrical connection cable 14 without contacting electrically the first and second conductive elements 14a, 14b, but rather contacting just the insulating sheath 14c. Moreover, the electrodes 20 extend through the adhesive layer set between the bottom surface 12a and the insulating sheath 14c, if this is present.
As previously mentioned, and as shown in FIG. 1a, in use the external unit 2 is set in the proximity of the eye, inside which the internal unit 4 is located. For example, the external unit 2 can be mounted on a pair of glasses, in such a way that the first antenna 8 is arranged within a lens of the pair of glasses, and in particular is arranged along the edge of said lens so as to enable the light to penetrate the eye. The transmitter 6 can be carried by an arm of the glasses.
The internal unit 4 is set inside the eye in such a way that the second antenna 10 is arranged in the proximity of the crystalline lens, possibly surrounding part of the crystalline lens itself.
The integrated electronic device 12 is arranged in the proximity of the retina of the eye, and in particular is arranged in such a way that the electrodes 20 will contact a portion of retina traversed by the optical axis of the crystalline lens, opposite to the pupil and including the so-called macula. Finally, the electrical connection cable 14 is arranged so as to pass along the inner wall of the bulb of the eye, without crossing the optical axis of the crystalline lens.
In greater detail, the second antenna 10 is arranged so as not to obstruct the path of the light rays that traverse the crystalline lens, and hence so as to enable the light that penetrates through the crystalline lens to reach the retina. Consequently, the second antenna 10 is arranged so as to surround the optical axis of the crystalline lens. In practice, in the case where the second antenna 10 is formed by a coil of conductive material, the axis of said coil coincides, to a first approximation, with the optical axis of the crystalline lens, which, amongst other things, intercepts the integrated electronic device 12.
In this way, the light coming from the outside world traverses the crystalline lens without undergoing significant alterations on account of the presence of the second antenna 10, and impinges on the integrated electronic device 12, and in particular on the photodetectors 18, which generate corresponding electrical signals, which in turn are supplied to the electronic circuitry 19. On the basis of the electrical signals supplied by the photodetectors 18, the electronic circuitry 19 generates, on the electrodes 20, corresponding electrical stimulation signals, which stimulate electrically the portion of retina in contact with the electrodes 20. In particular, the electrodes 20 stimulate the so-called internal retina (designated by 22 in FIG. 1b), which is formed, amongst other things, by the ganglion cells, the axons of which form the optical nerve. In this way, the retinal prosthesis 1 makes up, at least in part, for a possible reduced functionality of the so-called photoreceptor cells (designated by 24 in FIG. 1b), which include the cones and rods. In fact, since the ganglion cells are arranged between the photoreceptor cells 24 and the electrodes 20, the electrical stimulation signals do not traverse the photoreceptor cells 24, but rather directly stimulate the optical nerve.
In order to supply the integrated electronic device 12, the transmitter 6 generates a supply signal of an electromagnetic type, which is irradiated by the first antenna 8 and received by the second antenna 10 in such a way that, after prior propagation along the electrical connection cable 14, the supply signal reaches the integrated electronic device 12, supplying thereto the power necessary for its operation.
In greater detail, according to the frequency of the supply signal and to the distance between the first and second antennas 8, 10 a coupling of a magnetic or electromagnetic type is formed in such a way that a transfer of electric power occurs from the first antenna 8 to the second antenna 10. The electric power present on the second antenna 10 is then transferred to the integrated electronic device 12. In greater detail, in the particular case of magnetic coupling, the first and second antennas 8, 10 function as primary and secondary of a transformer.
Retinal prostheses similar to the retinal prosthesis 1, hence of an epiretinal type, are described, by way of example, in “Novel Retinal Prosthesis System with Three Dimensionally Stacked LSI Chip”, European Solid-State Device Research Conference, 2006, by Watanabe T. et al., or else in U.S. Pat. No. 6,976,998.
In general, retinal prostheses are known in which, instead of the integrated electronic device 12, a so-called system in package (SiP) is present, or else a stack of integrated circuits, also known as three-dimensional integrated circuit (3D IC). In addition, the electrodes 20 can form an array of electrodes structurally separate from the integrated electronic device 12.
Furthermore, retinal prostheses are known of the type described in US20060282128, where the external unit comprises a system for acquisition and processing of images, which are transmitted to the internal unit by means of coupling between the first antenna and the second antenna. In this case, the integrated electronic device may not comprise any photodetector.
Likewise known are retinal prostheses, and more precisely subretinal prostheses, of the type described in U.S. Pat. No. 7,483,750, where the electrodes are arranged between the internal retina and the external retina.
Once again with reference to the retinal prosthesis 1, this makes possible, after implant, to make up at least in part for a reduced functionality of the photoreceptor cells 24. However, in the case where the integrated electronic device 12 undergoes damage and has to be replaced, it becomes necessary to extract from the eye the entire internal unit 4.